Abstract
Two new sensitive spectrophotometric methods are reported for determination of tartrazine (Tz) (E102) in some commercial food samples. The first method involves two coupled reactions, the reduction of Cu(II) to Cu(I) by the analyte in acetate buffer medium (pH = 5.9) at 30°C and the complexation reaction between Cu(I) and Tz oxidized form to yield Cu-Tz complex (method I). The other method is based on oxidation of Tz by alkaline KMnO4. These reactions are monitored spectrophotometrically at maximum absorbances 332 and 610 nm for methods (I and II) respectively. Variables affecting these reactions are carefully studied and the conditions are optimized. The stability constants are calculated at 293, 303, 313 and 323 K. The thermodynamic parameters, Gibb’s free energy change (ΔG), entropy change (ΔS), and enthalpy change (ΔH) associated with the complexation reaction are calculated and discussed. Under optimized conditions the proposed methods (I, II) obey Beer’s law 10.69 - 85.50, 5.34 - 34.12 μg·ml-1 of Tz respectively. The molar absorptivity, sandel sensitivity, detection and quantification limits are calculated. Matrix effects are also investigated. The methods are successfully applied to the quantification of Tz in different commercially food samples. The results obtained are in good agreement with those obtained by the reported methods at the 95% confidence level.
Highlights
Food dyes are often added to foodstuffs and drinks in order to supply, intensify or restore their colour to create the desired coloured appearance [1]
The first method is based on oxidation of tartrazine by Cu(II) in acetate-acetic acid medium at 30 ̊C followed by complex formation
The electronic spectra of Tz in aqueous medium within pH 7.2 - 10.4 exhibit a broad band at 400 nm with a shoulder at 425 nm corresponding to tautomeric equilibria of monoanionic form of tartrazine salt (L4−), Scheme 1
Summary
Food dyes are often added to foodstuffs and drinks in order to supply, intensify or restore their colour to create the desired coloured appearance [1]. According to the limitations of European Union [EU] and Federal Food, Drug and Cosmetic Act [2], the presence and content of Tz dye must be controlled in food products due to their potential harmfulness to human beings [3]. It appears to cause the most allergic and intolerance reaction of all the azo dyes, among asthmatics and those with an aspirin intolerance [4] [5]. The other method is based on oxidation of Tz with alkaline KMnO4 under optimum conditions
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